"Boost; mechanic of Cloudsdale Weather factory, inventor of the hydrogen rocket pack, or High Altitude Initiation/Lander device (HAIL), and hopeful Solar Knight!" ~His self introdution
Boost is a young adult Unicorn living below Cloudsdale, in a district known as Cotton Cross. Thanks to having a Cloudwalking spell, he is one of the few non-pegasus ponies to work in Cloudsdale, and is currently employed as a mechanic in the Weather Factory, where his use of Levitation magic sets his mechanical mind a small step above his peers. However, his real dream is to become a pegasus knight in Celestia's service; something which may finally be realized with the creation of his rocket-pack, the HAIL.
Boost can be a bit proud of himself at times, though usually with good reason; since he has worked his way up from having absolutely nothing. Still, he at least realizes he's far from perfect, and works hard to become worthy of being called a knight. Outside of this, he can be a bit impatient, and would rather make things happen on his own rather than wait them out; which may or may not be a good thing depending on the circumstances.
The HAIL is probably Boost's single most recognizable feature, and he is rarely seen without it. To an untrained eye, it appears to be just a suit of pony guard attire with some pipes welded on, but in reality, it is so much more. Beneath the chest-plate of the armor are two large tanks of water. These lead into two small tanks on the side of the machine; here the lightning battery that's mounted on his back releases its charge from two transformers, and ionizes the water into hydrogen gas. From here, another pipe takes it to a chamber where it can be safely ignited and turned into propulsion. All operations are handled by a series of valves and switches he operates using his levitation magic.
Such a flight mechanism leaves it jerky in the air, and it is in no way meant for gliding. Once fired, it will take you where it was pointed, and then you're falling. For the most part, this means you're constantly firing it off and on, only falling while the battery powers up the transformer again.
To circumvent this bumpy sort of ride, Boost created two fold-able lightning rods to take advantage of the static electricity found in clouds and at high altitude, allowing the rockets to continually fire for long periods of time. For fun, and a minor enhancement, he webbed chain-links between them and the battery, making these collectors appear as metal wings. By continually firing like this, he has been able to attain speeds just 160 miles per hour slower than Mach 1 (Roughly 600 MPH), ranking him as probably the third or fourth fastest thing in Equestria... But to do so requires either a hurricane, or several minutes above the cloud layer.
Boost has also had his helmet reinforced, and extended to encase his horn. Doing so means he can use it as a short lance, if need be, though he never has used it on anything but a training dummy. Other than this and an extra layer of wool padding, his armor is exactly the same as a guard pony's.
He has also since then created special directional controllers to help control the angle of the thrust. Using these, he can go into rocket assisted flips, rolls and spins, greatly improving maneuvering options.
Boost was originally born in Canterlot to a pair of lower class unicorns. In his childhood, he dreamed of adventure, and a life better than the poverty he was born into. He two best friends, Drift and Aura Tracer further enhanced this want for adventure with tales of their travels with their families. After all, Drift was the son of the head of Canterlot's weather team, so he often traveled back to Cloudsdale, and Aura tracer was in a gypsy caravan, so between the two of them, he heard many stories about fantastic locations. Sadly, since both his parents had full-time jobs though, he never saw much outside of Canterlot.
That is, until Drift learned his special talent. With his new found ability to create clouds on the fly, the pegasus attempted a rather dirty trick in one of their play fights, and engulfed him in a cloud. While wandering the fog, he wished that he could simply get above it somehow... And lo and behold, his horn obliged, and introduced him to the magic of walking on clouds. Strangely, in a departure from the norm, he didn't get his cutie mark upon the discovery of his special spell.
Instead, it wasn't until he decided to try out his spell on a larger scale, and take a visit to Cloudsdale. The plan was that using his spell, he would stand on a cloud pushed by Drift. His friend reluctantly agreed, but only under the condition that he wear one of the flight school's training parachutes.
Once there, Boost of course wanted to see everything his friend had talked about, and eventually they made their way to the weather factory. Boost took a special interest in the cloud-making section of the factory; though not in the clouds themselves. He was entranced by the inner workings of the machines, and studied them with a curious eye. So judging himself an expert, when he found one of the machines that wasn't working, he went against his friend's advice and tried to repair it. Instead, he optimized it, and increased its output by 12%.
Realizing this, he earned his cutie mark-... And promptly also learned that his spell had a time limit. After dropping in and out of every building below the factory, he pulled his chute, and began making plans to one day live at the sky city.
Development of the HAIL
As Boost grew, and continued work at the weather factory, the length of time his Cloudwalking spell lasted grew as well, but it was far from perfect, and he still had to wear the Flight School's parachutes, and was well used to apologizing to everypony for punching holes in their ceilings. After all, he couldn't open a parachute until he was well clear of the rest of the city, and he still relied heavily on his friend for transport up to his job.
One day, the solution came to him on his job; a tarp from one of the weather storage sites blew into the cloud making area. Since he couldn't fly himself, there wasn't much he could do but watch as it blew over one of the cloud machines, and hitched a ride on a freshly-made cloud. He laughed as his co-workers clumsily attempted to wrestle it off the cloud, which unwittingly turned into a fight to hold the cloud down too. But he realized, if it took sixteen pegasus to fight one newborn cloud of that size, a tiny balloon filled with a new cloud could surely support him.
Well, assuming that he could make a new cloud without a massive generator. He understood that much of the machine could be condensed, since much of it was used to increase the output and longevity of the machine... But it still required lightning energy to run; something he couldn't even create himself.
The solution was a battery, a new device that was being developed to store said energy... But the current version, although small enough to carry, put out too small of a charge to create a cloud very fast, and he figured if it took 30 seconds to make this cloud, he'd be better off with parachutes!
Still he didn't give up just yet, and shortly found a way to make the battery output a much higher voltage, if only for a second at a time, but that was all he needed. However, what he failed to realize was that by increasing the charge, he wouldn't speed up the evaporation of the cloud solution, but rather ionize it into hydrogen gas-... Then all it took was one stray spark to turn the thing into a rocket.
One warehouse later, he began to work on using this rocket to instead propel him through the air, and he soon came up with a working prototype that could even recharge itself by flying through clouds or the ozone at high speed... But unless he was charging using the latter, the rockets still only could fire in short blasts, and hovering was impossible. He dubbed the machine the High Altitude Initiation/Landing device, or HAIL for short.
At least this reignited a childhood dream of becoming a knight in Celestia's service, and he has fashioned its design after their armor.
Expansion into Ponyville
Technically, more like a move to Ponyville. Shortly after returning from a campaign with Wisla, Boost found out he had lost his job at the weather factory. Unable to pay rent on his building there, he has instead moved the entirety of his repairs business to Ponyville.
His shop isn't officially open yet (nor does he have a name for it), but he's already working on some things, and will likely open soon.
Boost's design is largely inspired by the classic Sega game "Rocket Knight Adventures" which features a hero with a rocket pack of similar functionality to the HAIL, requiring the player to charge it for a moment before blasting into the air or enemies.